Sig Fig Review_2006 - CHEM 25 A Review of Significant...

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CHEM 25 A Review of Significant Figures It is impossible, in practice, to make an absolutely exact scientific measurement, because a process of comparison with some standard is involved, rather than a counting process. For example, the measurement of five mL of water with a typical 25 mL graduated cylinder would probably yield results varying between 4.8 and 5.2 mL, due to uncertainty in reading the meniscus of the liquid relative to the calibration marks on the cylinder. The average result would be properly expressed as 5.0 mL or 5.0 ± 0.2 mL, but would not be proper if expressed as 5.00 or 5 mL. In this case, the measurement justifies two significant figures, since the total number of significant figures justified in the measurement includes one (but no more than one) uncertain figure. For example, if a certain weight is given as 50.4 g, it may be assumed that the true value is definitely between 50 and 51 g and possibly between 50.3 and 50.5 g, but this weight cannot be assumed to be between 50.35 and 50.45 g, if the weight is properly expressed using
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